In recent years, power generating methods for generating clean and renewable energy have been progressed to cope with fear of exhaustion of oil energy and environmental problem. As representative examples, wind power generation and solar-light-condensing power generation are mentioned. Wind power generation has already been practically used in Europe and Asia, but it has a problem that power-generation quantity significantly decreases when wind speed decreases. Further, in the solar light-condensing power generation which is a method of condensing solar light by using a parabolic mirror to obtain solar energy and using the solar energy to produce high-temperature vapor for driving a power generator. However, it has a problem that sufficient solar energy can not be obtained when sun light is prevented by cloud.
Recently as a new power generation method, a power generating system using solar energy called solar chimney has been proposed (for example, Non-Patent Document 1). This power generating system using solar energy has a construction comprising a circular heat collector having a diameter of 4 km and having a chimney of 1 km high in the center. The heat collector has a structure like a greenhouse having no peripheral wall. The heat collector is configured so that air heated in the heat collector moves inside a roof of the heat collector towards the center to which the slope is sloping up, and reaches the highest point at the center. The heated air is drawn into the chimney disposed at the center of the heat collector. At this time, a wind-power generating turbine disposed in the chimney generates electric power. Since the temperature in the heat collector is higher than the outside temperature in the solar chimney system, air flow is generated by the heated air in the heat collector and power-generation is continued even if sun light is prevented by cloud. Further, by disposing a heat accumulator in the heat collector, power-generation is possible even in night time by heating air by heat irradiation from the heat accumulator.
Further, in a solar light-condensing power generation, instead of a conventional method of condensing solar light into one point by a parabolic mirror, an improved solar light-condensing power generation method is proposed (for example, refer to Patent Document 1), according to which a curved rectangular mirror is used to condense solar light into a linear shape to produce a large quantity of high-temperature vapor at one time.
Non-Patent Document 1 describes that a vinyl resin can be used as a covering material to be used for a solar thermal power generation system. In a case where a material having insufficient weather-resistance is used as a covering material for a heat collector of a solar chimney which is intended to supply electric power almost permanently, periodic replacement is required and cost for such a replacing work of a roof of the heat collector having a large area, becomes high. As a result, there is a problem that power-generation cost is increased. Further, the wind pressure of air heated in the heat collector increases as the air moves toward the center. Therefore, when a material having insufficient mechanical strength is employed, support-structures have to be installed at a small interval, which causes a problem that solar light is blocked by such support-structures to reduce power-generation efficiency. On the other hand, in a case where a glass excellent in weather-resistance and mechanical strength, is employed, thick support-structures have to be provided at a small interval to support the weight of the glass, which causes a problem that solar light is blocked to reduce power-generation efficiency.
Therefore, in a solar thermal power generation system, development of a covering material excellent in mechanical strength, weather resistance and transparency, has been desired.
Patent Document 1: JP-A-2002-115917
Non-Patent Document 1: NEDO International Report No. 869 (published on Nov. 19, 2001)